Surface electrode multiple mode operation

ABSTRACT

A surface electrode for ablating tissue is provided. The surface electrode comprises a base, a plurality of tissue penetrating needle electrodes extending from the surface of the base an adjustable distance, and an electrical interface coupled to the plurality of needle electrodes. The adjustability of the needle electrodes allows the depth that the needle electrodes penetrate through tissue to be adjusted.

FIELD OF THE INVENTION

The field of the invention relates generally to the use of ablationdevices for the treatment of tissue, and more particularly, RF ablationdevices for the treatment of tumors.

BACKGROUND OF THE INVENTION

The delivery of radio frequency (RF) energy to target regions withintissue is known for a variety of purposes. Of particular interest to thepresent invention, RF energy may be delivered to diseased regions intarget tissue for the purpose of causing tissue necrosis. For example,the liver is a common depository for metastases of many primary cancers,such as cancers of the stomach, bowel, pancreas, kidney, and lung.Electrosurgical probes with deploying electrode arrays have beendesigned for the treatment and necrosis of tumors in the liver and othersolid tissues. See, for example, the LeVeen™ Needle Electrode availablefrom Boston Scientific Corporation, which is constructed generally inaccord with U.S. Pat. No. 6,379,353, entitled “Apparatus and Method forTreating Tissue with Multiple Electrodes.”

The probes described in U.S. Pat. No. 6,379,353 comprise a number ofindependent wire electrodes that are deployed into tissue from thedistal end of a cannula. The wire electrodes may then be energized in amonopolar or bipolar fashion to heat and necrose tissue within a definedvolumetric region of target tissue. Difficulties have arisen in usingthe multiple electrode arrangements of U.S. Pat. No. 6,379,353 intreating tumors that lay at or near the surface of an organ, such as theliver. Specifically, some of the tips of the electrode array can emergefrom the surface after deployment. Such exposure of the needle tipsoutside the tissue to be treated is disadvantageous in a number ofrespects. First, the presence of active electrodes outside of theconfinement of the organ being treated subjects other tissue structuresof the patient as well as the treating personnel to risk of accidentalcontact with the electrodes. Moreover, the presence of all or portionsof particular electrodes outside of the tissue being treated caninterfere with proper heating of the tissue and control of the powersupply driving the electrodes. While it would be possible to furtherpenetrate the needle electrode into the treated tissue, such placementcan damage excessive amounts of healthy tissue.

In response to these adverse results, a device for ablating a tumor ator near the surface of tissue has been developed. Specifically, asillustrated in FIG. 1, an ablation assembly 20 comprises a surfaceelectrode 22 and an electrosurgical probe 24, such as a LeVeen™electrode, that can be operated in a bipolar mode to ablate the tissuein contact with, and between a needle electrode array 26 mounted to thedistal end of the probe 24 and the surface electrode 22. As illustrated,the surface electrode 22 comprises a generally flat or planardisk-shaped plate 28 and a plurality of tissue penetrating electrodes 30that project perpendicularly from the plate 28. The surface electrode 22further comprises a central aperture 32 that extends through the plate28, so that the surface electrode 22 can be threaded over the probe 24and locked into place about the deployed probe 24. The ablation assembly20 can then be operated in a monopolar or bipolar mode to ablate thetissue in contact with, and between, the electrode array 26 of the probe24 and the needles electrodes 30 of the surface electrode 22. Furtherdetails regarding these types of ablation devices are disclosed in U.S.Pat. No. 6,470,218, entitled “Apparatus and Method for Treating TumorsNear the Surface of an Organ,” which is hereby fully and expresslyincorporated herein by reference.

Although the ablation assembly illustrated in FIG. 1 is generally usefulin ablating superficially oriented tumors, it cannot be used toefficiently and safely ablate such tumors in all circumstances. Forexample, if the tumor is quite close to the surface of the tissue,placement of the needle electrodes without exposing any metallic surfacecan be difficult. Also, it may not be practical to use the probeassembly when the tumors are quite shallow. In this case, the surfaceelectrode may be used by itself. Efficient ablation of the tumor,however, may not be achieved if the tumor has a non-uniform thickness.

There thus is a need to provide improved systems and methods for moreefficiently and safely ablating superficially oriented tumors.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present inventions, a surfaceelectrode for ablating tissue comprises a base, a plurality of tissuepenetrating needle electrodes extending from the surface of the base anadjustable distance, and an electrical interface coupled to theplurality of needle electrodes. By way of non-limiting example, theadjustability of the needle electrodes allows the depth that the needleelectrodes penetrate through tissue to be adjusted. In the preferredembodiment, the needle electrodes are individually adjustable, so thatthe depths at which the needle electrodes penetrate the tissue can bevaried. All or any portion of the needle electrodes carried by the basecan be adjustable.

In one preferred embodiment, the base takes the form of a flat plate,but can take the form of any structure from which needle electrodes canbe extended. In the preferred embodiment, the needle electrodes extendperpendicularly from the base, but can extend obliquely from the base aswell.

The needle electrodes can be mounted to the base in any variety ofmanners, so that the distance that the needle electrodes extend from thebase can be adjusted. For example, the needle electrodes can be mountedto the surface of the base in a threaded arrangement, such that rotationof each needle electrode in one direction increases the distance thatthe needle electrode extends from the surface of the base, and rotationof each needle electrode in the other direction decreases the distancethat the needle electrode extends from the surface of the base. Asanother example, the needle electrodes can be mounted to the surface ofthe base in a sliding arrangement, such that displacement of each needleelectrode in a distal direction increases the distance that the needleelectrode extends from the surface of the base, and displacement of eachneedle electrode in a proximal direction decreases the distance that theneedle electrode extends from the surface of the base. In this case, thesurface electrode may further comprise one or more locking mechanisms(e.g., thumb screws) for fixing displacement of the needle electrodesrelative to the surface of the base.

The electrical interface may be configured, such that the ablationenergy is delivered to the needle electrodes in the desired manner. Forexample, the electrical interface may couple the needle electrodes in amonopolar or bipolar arrangement. The electrical interface mayoptionally be adjustable, so that certain needle electrodes can beselectively activated or combinations of needle electrodes can beselectively placed in a bipolar arrangement with respect to each other.

The surface electrode may optionally comprise insulation to minimizeinadvertent ablation of healthy tissue. For example, the surface of thebase from which the needle electrodes extend may be electricallyinsulated. Or the surface electrode may further comprise a plurality ofelectrically insulating sleeves extending from the surface of the base,wherein the insulating sleeves encompass portions of the respectiveneedle electrodes. The insulating sleeves may be optionally extendablefrom the surface of the base an adjustable length. By way ofnon-limiting example, the adjustability of the insulating sleeves allowsthe depth at which healthy tissue is protected to be adjusted.

One or more of the plurality of needle electrodes can comprise a liquidconveying lumen to carry a medium for cooling, therapeutic, or otherpurposes. For example, the lumen(s) can be configured to perfuse amedium from, and/or internally convey a medium within, the respectiveneedle electrode(s).

In accordance with a second aspect of the present inventions, a tissueablation system comprises a surface electrode comprising a base and aplurality of tissue penetrating needle electrodes extending from thesurface of the base an adjustable distance, and an ablation source(e.g., a radio frequency generator) coupled to the plurality of needleelectrodes. The surface electrode can be configured in the same mannerdescribed above.

The tissue ablation system can be operated in a monopolar mode or abipolar mode. For example, the tissue ablation system can furthercomprise a dispersive electrode, wherein the radio frequency generatorcomprises a first pole electrically coupled to the surface electrode anda second pole electrically coupled to the dispersive electrode. Asanother example, the first pole of the radio frequency generator can beelectrically coupled to a first set of the plurality of needleelectrodes and the second pole can be electrically coupled to a secondset of the plurality of needle electrodes. If any of the needleelectrodes is configured to convey a medium, the tissue ablation systemcan further comprise a source of medium (e.g., a pump) in fluidcommunication with the lumen of the respective needle electrode.

In an optional embodiment, the tissue ablation system can furthercomprise a clamping device having first and second opposing arms. Inthis case, the surface electrode can be mounted to one of the arms, anda similar surface electrode can be mounted to the other of the arms. Thetissue ablation system can be operated in a bipolar mode by connectingthe first pole of the radio frequency generator to the first surfaceelectrode and the second pole to the second surface electrode.Alternatively, a second surface electrode is not provided, but rather asupport member with or without tissue penetrating needles. In this case,the support member is used merely to stabilize contact between thesurface electrode and the tissue.

In accordance with a third aspect of the present inventions, a method ofablating tissue using a surface electrode with a plurality of needleelectrodes is provided. The method comprises adjusting distances thatthe needle electrodes extend from a base of the surface electrode,penetrating the tissue with the needle electrodes, and conveyingablation energy from the needle electrodes into the tissue (e.g., in amonopolar or bipolar mode) to create a lesion on the tissue. The needleelectrode distances can be adjusted prior to, and/or subsequent to,penetrating the tissue with the needle electrodes. Optionally, theneedle electrodes from which the ablation energy is conveyed can bedynamically selected.

In the preferred method, the needle electrode distances are individuallyadjusted, in which case, the needle electrode distances may differ fromeach other. These needle electrode distances can be adjusted in avariety of manners, e.g., by rotating the needle electrodes orlongitudinally sliding the needle electrodes relative to the base.

In order to, e.g., protect healthy tissue, the surface electrode can beinsulated by insulating the base and/or insulating portions of theneedle electrodes that would otherwise be in contact with the tissue,e.g., by insulating the needle electrode portions with insulationsleeves that extend from the surface of the base. In this case, thedistances from which the insulation sleeves extend from the surface ofthe base can be adjusted.

The method optionally comprises conveying a medium through one or moreof the plurality of needle electrodes. For example, the medium can beperfused from the needle electrode(s) into the tissue (e.g., to cool thetissue and/or deliver a therapeutic agent to the tissue) and/orinternally conveyed within the needle electrode(s) to cool the needleelectrode(s).

In another optional method, the tissue can be penetrated with aplurality of needle electrodes of another surface electrode opposite theneedle electrodes of the first surface electrode, in which case, theablation energy may be conveyed from the other needle electrodes intothe tissue. If RF energy is used as the ablation energy, the ablationenergy can be conveyed between the first and second surface electrodes.In addition, the needle electrode distances of the second surfaceelectrode can be adjusted in the same manner as the needle electrodedistances of the first surface electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of a preferred embodimentof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate the advantagesand objects of the present invention, reference should be made to theaccompanying drawings that illustrate this preferred embodiment.However, the drawings depict only one embodiment of the invention, andshould not be taken as limiting its scope. With this caveat, theinvention will be described and explained with additional specificityand detail through the use of the accompanying drawings in which:

FIG. 1 is a perspective view of a prior art ablation assembly;

FIG. 2 is plan view of a tissue ablation system constructed inaccordance with one preferred embodiment of the present inventions;

FIG. 3 is a perspective view of one preferred embodiment of a surfaceelectrode that can be used in the tissue ablation system of FIG. 2,wherein an electrical interface that can configure the needle electrodesin a monopolar arrangement is particularly shown;

FIG. 4 is a cross-sectional view of the surface electrode of FIG. 3,wherein adjustment of needle electrodes are accomplished using athreaded arrangement;

FIG. 5 is a cross-sectional view of the surface electrode of FIG. 3,wherein adjustment of needle electrodes are accomplished using a slidingarrangement;

FIG. 6 is a perspective view of another preferred embodiment of asurface electrode that can be used in the tissue ablation system of FIG.2, wherein an electrical interface that can configure the needleelectrodes in a bipolar arrangement is particularly shown;

FIG. 7 is a perspective view of a still another preferred embodiment ofa surface electrode that can be used in the tissue ablation system ofFIG. 2, wherein adjustable insulated sleeves are used to insulateportions of the needle electrodes;

FIG. 8 is a cross-sectional view of the surface electrode of FIG. 7,wherein adjustment of needle electrodes is accomplished using a threadedarrangement;

FIG. 9 is a cross-sectional view of the surface electrode of FIG. 7,wherein adjustment of needle electrodes is accomplished using a slidingarrangement;

FIGS. 10-13 are plan views illustrating one preferred method of usingthe tissue ablation system of FIG. 1 to ablate a treatment region withintissue of a patient;

FIG. 14 is plan view of a tissue ablation system constructed inaccordance with another preferred embodiment of the present inventions;

FIG. 15 is a cross-sectional view of one preferred embodiment of aneedle electrode that can be used in the tissue ablation system of FIG.14;

FIG. 16 is a cross-sectional view of another preferred embodiment of aneedle electrode that can be used in the tissue ablation system of FIG.14;

FIG. 17 is a perspective view of a preferred embodiment of a surfaceelectrode that can be used in the tissue ablation system of FIG. 15;

FIG. 18 is plan view of a tissue ablation system constructed inaccordance with still another preferred embodiment of the presentinventions; and

FIGS. 19-20 are plan views illustrating one preferred method of usingthe tissue ablation system of FIG. 18 to ablate a treatment regionwithin tissue of a patient.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 illustrates a tissue ablation system 100 constructed inaccordance with a referred embodiment of the present invention. Thetissue ablation system 100 generally comprises a surface electrode 102,which is configured to be applied to the surface of tissue, e.g., anorgan, in order to ablate target tissue therein, and a radio frequency(RF) generator 104 configured for supplying RF energy to the surfaceelectrode 102 via a cable 106 in a controlled manner. In the embodimentillustrated in FIG. 2, only one surface electrode 102 is shown. As willbe described in further detail below, however, multiple surfaceelectrodes 102 can be connected to the RF generator 104 depending uponthe specific ablation procedure that the physician selects.

Referring further to FIG. 3, the surface electrode 102 generallycomprises a base 108 having a flat surface 110, an array of needleelectrodes 112 extending from the surface 110 of the base 108, and anelectrical interface 114 for electrically coupling the needle electrodes112 to the RF generator 104.

In the illustrated embodiment, the base 108 takes the form of a flatrectangular plate, but other shapes (e.g., circular, oval, quadrangular)can be used, depending upon the nature of the tissue to be ablated.Exemplary bases will have a length in the range of 10 mm to 100 mm,preferably from 30 mm to 60 mm, a width in the range of 10 mm to 100 mm,preferably from 30 mm to 60 mm, and a thickness in the range of 1 mm to20 mm, preferably from 5 mm to 15 mm. Preferably, the base 108 iscomposed of a rigid material, such as, e.g., Acrylonitrile ButadieneStyrene (ABS), polycarbonate, polyvinylchloride (PVC), aluminum, orstainless steel. In this manner, application of force on any flatportion of the base 108 will uniformly distribute the force along thesurface 110 of the base 108, so that all of the needle electrodes 112will penetrate the tissue. In alternative embodiments, however, the base108 may be composed of a semi-rigid or flexible material. In thismanner, the base 108 can be conveniently conformed to the curved surfaceof tissue. In this case, the force needed to penetrate the tissue withthe needle electrodes 112 can be applied to the base 108 in a uniformlydistributed manner, e.g., using the entire palm of a hand, or can beserially applied to portions of the base 108 so that the needleelectrodes 112 penetrate the tissue in a piece-meal fashion.

In any event, if the base 108 is composed of an electrically conductivematerial, a layer of insulation 116, e.g., rubber, is disposed on thesurface 110 of the base 108 using suitable means, such as bonding. Inthis manner, any ablation energy will be concentrated within the needleelectrodes 112, so that only the target tissue is ablated, therebypreventing non-target tissue, e.g., the surface of the tissue in contactwith the surface 110 of the base 108, from being ablated.

The needle electrodes 112 are composed of a rigid electricallyconductive material, e.g., stainless steel. The needle electrodes 112preferably have circular cross-sections, but may have non-circularcross-sections, e.g., rectilinear cross-sections. Exemplary needleelectrodes will have a diameter in the range of 0.6 mm to 3.4 mm,preferably from 1.1 mm to 1.6 mm, and a length in the range of 10 mm to70 mm, preferably from 20 mm to 50 mm. The distal ends of the needleelectrodes 112 may be honed or sharpened to facilitate their ability topenetrate tissue. The distal ends 118 of these needle electrodes 112 maybe hardened using conventional heat treatment or other metallurgicalprocesses. The needle electrodes 112 are covered with insulation (notshown), although they will be at least partially free from insulationover their distal ends 118. As will be described in further detailbelow, the portion of the needle electrodes 112 that can be placed incontact with the base 108 are also free of insulation.

In the illustrated embodiment, the RF current is delivered to the needleelectrodes 112 in a monopolar fashion. Therefore, the current will passthrough the needle electrodes 112 and into the target tissue, thusinducing necrosis in the tissue. To this end, the needle electrodes 112are configured to concentrate the energy flux in order to have aninjurious effect on tissue. However, there is a dispersive electrode(not shown) which is located remotely from the needle electrodes 112,and has a sufficiently large area—typically 130 cm² for an adult—so thatthe current density is low and non-injurious to surrounding tissue. Inthe illustrated embodiment, the dispersive electrode may be attachedexternally to the patient, using a contact pad placed on the patient'sskin.

Alternatively, the RF current is delivered to the needle electrodes 112in a bipolar fashion, which means that current will pass between“positive” and “negative” electrodes 112. As will be described infurther detail below, RF current can also pass between needle electrodes112 of two or more surface electrodes 102 in a bipolar fashion.

The lengths of the needle electrodes 112 are adjustable, i.e., theneedle electrodes 112 extend from the surface 110 of the base 108 anadjustable distance. Specifically, in the illustrated the proximal ends120 of the needle electrodes 112 are mounted within apertures 122 formedthrough the base 108 in a threaded arrangement. As best shown in FIG. 4,the shafts of the needle electrodes 112 and the respective apertures 122formed through the base 108 include threads 124, such that rotation ofthe needle electrodes 112 in one direction 126 (here, in thecounterclockwise direction) decreases the distances that the needleelectrodes 112 extend from the surface 110 of the base 108, and rotationof the needle electrodes 112 in the opposite direction 128 (here, in theclockwise direction) increases the distances that the needle electrodes112 extend from the surface 110 of the base 108. As can be appreciated,the lengths of the needle electrodes 112 are individually adjustable, sothat the distances that the respective needle electrodes 112 extend fromthe surface 110 of the base 108 may differ, as clearly shown in FIG. 4.

Alternatively, as illustrated in FIG. 5, the shafts of the needleelectrodes 112 can be slidably mounted within the apertures 122 formedthrough the base 108, so that longitudinal translation of the needleelectrodes 112 relative to the apertures 122 in the distal direction 130increases the distances that the needle electrodes 112 extend from thesurface 110 of the base 108, and longitudinal translation of the needleelectrodes 112 relative to the apertures 122 in the proximal direction132 decreases the distances that the needle electrodes 112 extend fromthe surface 110 of the base 108. In order to fix the needle electrodes112 relative to the base 108, the base 108 comprises bosses 134 formedalong its opposite surface 111. Each of the bosses 134 comprises athreaded hole 136 with an associated thumb screw 138. Thus, the shaftsof the needle electrodes 112 can be affixed within the bosses 134 bytightening the thumb screws 138, and released within the bosses 134 byloosening the thumb screws 138.

Referring back to FIG. 3, the electrical interface 114 provides a meansfor selectively configuring the needle electrodes 112. For example, in amonopolar arrangement where all of the needle electrodes 112 are coupledto a first pole of the RF generator 104 and a separate dispersiveelectrode (not shown) is coupled to a second pole of the RF generator104, the electrical interface 114 can comprise a single dip switch 140coupled to the first pole of the RF generator 104. In this manner, thedip switch 140 can be operated to selectively turn each needle electrode112 on or off, so that RF energy will be conveyed between some of theneedle electrodes 112 and the dispersive electrode, and will not beconveyed between others of the needle electrodes 112 and the dispersiveelectrode.

In a bipolar arrangement where some of the needle electrodes 112 arecoupled to the first pole of the RF generator 104 and others of theneedle electrodes 112 are coupled to the second pole of the RF generator104, the electrical interface 114 can take the form of a pair of dipswitches 140′ and 140″ respectively coupled to the two poles of the RFgenerator 104, as illustrated in FIG. 6. In this manner, the first dipswitch 140′ can be operated to turn a first subset of needle electrodes112 on, and the second dip switch 140″ can be operated to turn a seconddifferent subset of needle electrodes 112 on, so that RF energy will beconveyed between the first and second subsets of needle electrodes 112.

Whether the needle electrodes 112 are operated in a monopolar mode orbipolar mode, the electrical interface 114 is coupled to the respectiveneedle electrodes 112 by electrical paths 144 that are preferablyelectrically isolated from each other. This can be accomplisheddepending on the means that is used for adjusting the lengths of theneedle electrodes 112. For example, if the lengths of the needleelectrodes 112 are adjusted by rotating the needle electrodes 112 withinthe respective apertures 122, the electrical paths can compriseelectrical traces (shown in FIG. 3) that extend along the oppositesurface 111 of the base 108 between the electrical interface 114 and theapertures 122 in which the shafts of the needle electrodes 112 aremounted. In this case, the base 108 can be composed of an electricallynon-conductive material, in which case, the apertures 122 can be coatedwith an electrically conductive material, such as, e.g., gold or copper.If the lengths of the needle electrodes 112 are adjusted bylongitudinally translating the needle electrodes 112 within therespective apertures 122, the electrical paths 144 can compriseinsulated wires (not shown) that extend between the electrical interface114 and the proximal ends 120 of the needle electrodes 112.

It should be noted, however, that if selective arrangement of the needleelectrodes 112 is not desired, and the needle electrodes 112 are notoperated in a bipolar mode, the base 108 can be totally composed of anelectrically conductive material, in which case, the electricalinterface 114 can take the form of a simple connection that operates tocouple the cable 106 of the RF generator 104 to the apertures 122 (andthus the needle electrodes) through the base 108 itself.

In an optional embodiment of a surface electrode, the electricalinsulation associated with the needle electrodes 112 can be adjustable,so that the length of the electrically conductive portion of the needleelectrodes 112 that will be in contact with the tissue can be adjusted.For example, as illustrated in FIG. 7, an optional surface electrode 152is similar to the previously described surface electrode 102, with theexception that it comprises insulating sleeves 154 that are mountedwithin apertures 122 formed through the base 108.

The lengths of the insulating sleeves 154 are adjustable, i.e., thedistances that the insulating sleeves 154 extend from the surface 110 ofthe base 108 can be varied. Specifically, in the illustrated embodiment,the insulating sleeves 154 are mounted within apertures 122 formedthrough the base 108 in a threaded arrangement. As best shown in FIG. 8,the insulating sleeves 154 and the respective apertures 122 formedthrough the base 108 include threads 156, such that rotation of theinsulating sleeves 154 in the direction 126 decreases the distances thatthe insulating sleeves 154 extend from the surface 110 of the base 108,and rotation of the insulating sleeves 154 in the opposite direction 128increases the distances that the insulating sleeves 154 extend from thesurface 110 of the base 108.

As with the previously described surface electrode 102, the lengths ofthe needle electrodes 112 are also adjustable. In this case, theproximal ends of the needle electrodes 112 are mounted within insulatingsleeves 154 in a threaded arrangement. The shafts of the needleelectrodes 112 and the insulating sleeves 154 include threads 158, suchthat rotation of the needle electrodes 112 relative to the insulatingsleeves 154 in direction 126 decreases the distances that the needleelectrodes 112 extend from the surface 110 of the base 108, and rotationof the needle electrodes 112 relative to the insulating sleeves 154 inthe opposite direction 128 increases the distances that the needleelectrodes 112 extend from the surface 110 of the base 108.

Alternatively, as illustrated in FIG. 9, the shaft of the needleelectrodes 112 can be slidably mounted within the insulating sleeves154, so that longitudinal translation of the needle electrodes 112relative to the insulating sleeves 154 in the distal direction 130increases the distances that the needle electrodes 112 extend from thesurface 110 of the base 108, and longitudinal translation of the needleelectrodes 112 relative to the insulating sleeves 154 in the proximaldirection 132 decreases the distances that the needle electrodes 112extend from the surface 110 of the base 108. In order to fix the needleelectrodes 112 relative to the base 108, each of the insulating sleeves154 comprises a threaded hole 160 with an associated thumb screw 162.Thus, the shafts of the needle electrodes 112 can be affixed within theinsulating sleeves 154 by tightening the thumb screws 162, and releasedwithin the insulating sleeves 154 by loosening the thumb screws 162.

Whichever means is used to adjust the needle electrodes 112 within theinsulating sleeves 154, the lengths of the insulating sleeves 154 areindividually adjustable, so that the distances that the respectiveinsulating sleeves 154 extend from the surface 110 of the base 108, andthus, the lengths of the electrical portions of the needle electrodes112 that will be in contact with the tissue, may differ. In a similarmanner, the needle electrodes 112 are individually adjustable, so thatthe distances that the respective needle electrodes 112 extend from thesurface 110 of the base 108, and thus, the depths that they penetratetissue, may differ.

The insulating sleeves 154 are composed of a rigid electricallynon-conductive material, such as, e.g., fluoropolymer, polyethyleneterephthalate (PET), polyetheretherketon (PEEK), polyimide, and otherlike materials. Alternatively, the insulating sleeves 154 may becomposed of an electrically conductive material that is coated within anelectrically non-conductive material. If the lengths of the needleelectrodes 112 are adjusted by rotating the needle electrodes 112 withinthe respective apertures 122, the threaded portions of the insulatingsleeves 154 are preferably composed of an electrically conductivematerial to provide an electrical path between the shafts of the needleelectrodes 112 and the traces 144 extending along the opposite surface111 of the base 108. If the lengths of the needle electrodes 112 areadjusted by longitudinally translating the needle electrodes 112 withinthe insulating sleeves 154, the insulating sleeves 154 can be composedentirely of electrically non-conductive material, since the wiresleading from the electrical interface 114 can be coupled directly to theproximal ends 120 of the needle electrodes 112.

Referring back to FIG. 2, as previously noted, the RF generator 104 iselectrically connected, via the electrical interface 114, to the needleelectrodes 112. The RF generator 104 is a conventional RF power supplythat operates at a frequency in the range of 200 KHz to 1.25 MHz, with aconventional sinusoidal or non-sinusoidal wave form. Such power suppliesare available from many commercial suppliers, such as Valleylab, Aspen,and Bovie. Most general purpose electro-surgical power supplies,however, operate at higher voltages and powers than would normally benecessary or suitable for controlled tissue ablation.

Thus, such power supplies would usually be operated at the lower ends oftheir voltage and power capabilities. More suitable power supplies willbe capable of supplying an ablation current at a relatively low voltage,typically below 150V (peak-to-peak), usually being from 50V to 100V. Thepower will usually be from 20W to 200W, usually having a sine wave form,although other wave forms would also be acceptable. Power suppliescapable of operating within these ranges are available from commercialvendors, such as Boston Scientific of San Jose, Calif., which marketsthese power supplies under the trademarks RF2000™ (100W) and RF3000™(200W).

Having described the structure of the tissue ablation system 100, itsoperation in treated targeted tissue will now be described. Thetreatment region may be located anywhere in the body where hyperthermicexposure may be beneficial. Most commonly, the treatment region willcomprise a solid tumor within an organ of the body, such as the liver,kidney, pancreas, breast, prostrate (not accessible via the urethra),and the like. The volume to be treated will depend on the size of thetumor or other lesion, typically having a total volume from 1 cm³ to 150cm³, and often from 2 cm³ to 35 cm³. The peripheral dimensions of thetreatment region may be regular, e.g., spherical or ellipsoidal, butwill more usually be irregular. The treatment region may be identifiedusing conventional imaging techniques capable of elucidating a targettissue, e.g., tumor tissue, such as ultrasonic scanning, magneticresonance imaging (MRI), computer assisted tomography (CAT) fluoroscopy,nuclear scanning (using radiolabeled tumor-specific probes), and thelike. Preferred is the use of high resolution ultrasound of the tumor orother lesion being treated, either intraoperatively or externally.

Referring now to FIG. 10-12, the operation of the tissue ablation system100 is described in treating a treatment region TR, such as a tumor,located below the surface S of tissue T, e.g., an organ. The treatmentregion TR has a proximal surface S1 and a distal surface S2 opposite theproximal surface S1. As can be seen, the depth of the treatment regionTR varies below the surface S of the tissue. Thus, by itself, a surfaceelectrode having needle electrodes with uniform lengths will typicallynot optimally ablate the treatment region TR. The previously describedsurface electrode 102, however, can be used to optimally ablate thetreatment region TR when properly configured.

First, the electrical interface 114 on the surface electrode 102 isconfigured, based on the shape of the treatment region TR and whether amonopolar or a bipolar arrangement is desired. The surface electrode 102is then positioned onto the surface S of the tissue T directly above thetreatment region TR, and pressure is applied so that the needleelectrodes 112 penetrate into the tissue T, as illustrated in FIG. 11.Preferably, access to the tissue T is gained through a surgical openingmade through the skin of the patient. If the surface electrode 102 issmall enough or flexible enough, it can alternatively be introduced intocontact with the tissue T laparoscopically. Once the needle electrodes112 are embedded into the tissue T, the distances that the needleelectrodes 112 extend from the base 108 of the surface electrode 102 areindividually adjusted, so that the distal ends 118 of the needleelectrodes 112 penetrate through, or almost penetrate through, thedistal surface S2 of the treatment region TR, as illustrated in FIG. 12.As can be appreciated, the deeper a region of the distal surface S2 isbelow the surface of the tissue T, the greater the distance that theneedle electrode 112 associated with that region must extend from thebase 108 of the surface electrode 102.

If the surface electrode 152 with adjustable insulating sleeves 154 isused, the distances that the insulating sleeves 154 extend from the base108 of the surface electrode 102 are individually adjusted, so thedistal ends of the insulating sleeves 154 are just above the proximalsurface S1 of the treatment region TR, as illustrated in FIG. 13. As canbe appreciated, the deeper a region of the proximal surface S1 is belowthe surface of the tissue T, the greater the distance that theinsulating sleeve 204 associated with that region must extend from thebase 108 of the surface electrode 102. Thus, as can be seen, theelectrically conductive portions of the needle electrodes 112 are onlyin contact with the treatment region TR.

It should be noted that whichever surface electrode is used, thetreatment region TR can be monitored using suitable imaging means toensure that the needle electrodes 112 and/or insulating sleeves 154 areproperly adjusted. It should also be noted that gross adjustments of theneedle electrodes 112 and/or insulating sleeves 154 can be accomplishedprior to introducing the surface electrode 102 within the patient's bodyto minimize adjustments to the surface electrode 102 while it is in thepatient's body. In this case, fine adjustments of the needle electrodes112 and/or insulating sleeves 154 can be performed after the needleelectrodes 112 have been embedded into the tissue T.

Next, the RF generator 104 is connected to the electrical interface 114of the surface electrode 102, and then operated to ablate the treatmentregion TR, resulting in the formation of a lesion that preferablyencompasses the entirety of the treatment region TR. If the treatmentregion TR is substantially larger than that which the surface electrode102 can cover, thereby resulting in a treatment region TR that is onlypartially ablated, the surface electrode 102 can be moved to thenon-ablated portion of the treatment region TR, and the process can thenbe repeated. Alternatively, multiple surface electrodes 102 can be used,so that the large treatment region TR can be ablated in one step.

FIG. 14 illustrates a tissue ablation system 200 constructed inaccordance with another preferred embodiment of the present invention.The tissue ablation system 200 is similar to the previously describedtissue ablation system 100, with the exception that it provides coolingfunctionality. Specifically, the tissue ablation system 200 comprisesthe previously described RF generator 104, a surface electrode 202additionally configured to cool the target tissue while it is beingablated, and a pump assembly 204 configured for delivering a coolingmedium to the surface electrode 102.

The surface electrode 202 is similar to the surface electrode 102illustrated in FIG. 5, with the exception that it has coolingfunctionality. Specifically, the surface electrode 202 comprises needleelectrodes 212 that comprise cooling lumens through which a coolingmedium can be pumped. In the illustrated embodiment, two types of needleelectrodes 212 are used: an irrigated needle electrode 212(1) and aninternally cooled needle electrode 212(2). As illustrated in FIG. 15,the irrigated needle electrode 212(1) comprises a cooling lumen 218 thatoriginates at an entry port 220 at the proximal end 214 of the needleelectrode 212(1) and terminates at an exit port 222 at the distal end216 of the needle electrode 212(1). As a result, a cooling medium thatis conveyed through the entry port 220 and distally through the coolinglumen 218 is perfused out from the exit port 222 into the surroundingtissue, thereby cooling the tissue while it is being ablated. Asillustrated in FIG. 16, the internally cooled needle electrode 212(2)comprises a cooling lumen 224 that originates at an entry port 228 atthe proximal end 214 of the needle electrode 212(2) and a return lumen226 that terminates at an exit port 230 at the proximal end 214 of theneedle electrode 212(2). The cooling and return lumens 224 and 226 arein fluid communication with each other at the distal end 216 of theneedle electrode 212(2). As a result, a cooling medium is conveyed intothe entry port 228 and distally through the cooling lumen 224 to coolthe shaft of the needle electrode 212(2), with the resultant heatedmedium being proximally conveyed through the return lumen 226 and outthrough the exit port 230. It should be noted that for the purposes ofthis specification, a cooling medium is any medium that has atemperature suitable for drawing heat away from the surface electrode202. For example, a cooling medium at room temperature or lower is wellsuited for cooling the surface electrode 202.

Referring to FIG. 17, the surface electrode 202 further comprises afluid manifold 232 having an inlet fluid port 234 and an outlet fluidport 236 that are configured to be connected to the pump assembly 204,as will be described in further detail below. The fluid manifold 232further comprises an array of branch ports 238 that are in fluidcommunication with the inlet and outlet ports 234 and 236.

The surface electrode 202 further comprises an array of conduits 240that are respectively mounted at their proximal ends to the branchedports 238 of the cooling manifold 232 and at their distal ends toproximal ends 214 of the needle electrodes 212 in fluid communicationwith the lumens therein. The conduits 240 that are associated with theirrigated needle electrodes 212(1) each comprises a single cooling lumen(not shown) that is in fluid communication between the inlet port 234 ofthe cooling manifold 232 and the entry port 220 (shown in FIG. 15) ofthe respective needle electrode 212(1). The conduits 240 that areassociated with the internally cooled needle electrodes 212(2) eachcomprises a cooling lumen (not shown) that is in fluid communicationbetween the inlet port 234 of the cooling manifold 232 and the entryport 228 (shown in FIG. 16) of the respective needle electrode 212(2),and a return lumen (not shown) that is in fluid communication betweenthe outlet port 236 of the cooling manifold 232 and the exit port 230(shown in FIG. 16) of the respective needle electrode 212(2).

Referring back to FIG. 14, the pump assembly 204 comprises a power head242 and a syringe 244 that is front-loaded on the power head 242 and isof a suitable size, e.g., 200 ml. The power head 242 and the syringe 244are conventional and can be of the type described in U.S. Pat. No.5,279,569 and supplied by Liebel-Flarsheim Company of Cincinnati, Ohio.The pump assembly 204 further comprises a source reservoir 246 forsupplying the cooling medium to the syringe 244, and a dischargereservoir 248 for collecting the heated medium from the surfaceelectrode 202. The pump assembly 204 further comprises a tube set 250removably secured to an outlet 252 of the syringe 244. Specifically, adual check valve 254 is provided with first and second legs 256 and 258.The first leg 256 serves as a liquid inlet connected by tubing 260 tothe source reservoir 246. The second leg 258 serves as a liquid outletand is connected by tubing 262 to the inlet fluid port 234 on thecooling manifold 232 of the surface electrode 202. The dischargereservoir 248 is connected to the outlet fluid port 236 on the coolingmanifold 232 of the surface electrode 202 via tubing 264.

Thus, it can be appreciated that the pump assembly 204 can be operatedto periodically fill the syringe 244 with the cooling medium from thesource reservoir 246, and convey the cooling medium from the syringe244, through the tubing 262, and into the inlet fluid port 232 on thecooling manifold 232. The cooling medium will then be conveyed throughthe branched ports 238 of the cooling manifold 232, through the coolinglumens on the conduits 240 (shown in FIG. 17), and into the coolinglumens 218 and 224 in the respective needle electrodes 212(1) and 212(2)(shown in FIGS. 15 and 16). With respect to the irrigated needleelectrodes 212(1), the cooling medium will be perfused into the tissueto cool it. With respect to the internally cooled needle electrodes212(2), the cooling medium will be internally circulated within theneedle electrode 112 to cool it. The resultant heated medium will beconveyed from the return lumens 226 of the needle electrodes 212(2),through the return lumens of the conduits 240, and into the branchedports 238 of the cooling manifold 232. The heat medium will then beconveyed from the outlet fluid port 234 on the cooling manifold 232,through the tubing 264, and into the discharge reservoir 248.

Operation of the tissue ablation system 200 will be similar to that ofthe tissue ablation system 100, with the exception that the pumpassembly 204 will be operated to cool the target tissue and needleelectrodes 212. Optionally, the cooling medium can contain a therapeuticagent that can be delivered to the tissue via the irrigated needleelectrodes 212(2). The pump assembly 204, along with the RF generator104, can include control circuitry to automate or semi-automate thecooled ablation process.

FIG. 18 illustrates a tissue ablation system 300 constructed inaccordance with still another preferred embodiment of the presentinvention. The tissue ablation system 300 is similar to the previouslydescribed tissue ablation system 100, with the exception that itcomprises an ablative clamping device 302 that incorporates two surfaceelectrodes 102. In particular, the clamping device 302 comprises twoopposing clamping members 304 that are coupled to each other via a pivotpoint 306. The surface electrodes 102 are mounted to arms 308 of therespective clamping members 304, such that the needle electrodes 112 ofthe surface electrodes 102 oppose each other. The clamping members 304include handles 310 that, when closed, move the opposing needles 112 ofthe respective surface electrodes 102 away from each other, and whenopened, move the opposing needles 112 of the respective surfaceelectrodes 102 towards each other. Thus, it can be appreciated that theclamping device 302 can engage and penetrate tissue in an opposingmanner when the handles 310 of the clamping device 302 are opened, anddisengage the tissue when the handles 310 are closed.

The cables 106 of the RF generator 104 are coupled to the electricalinterfaces (not shown in FIG. 18) of the respective surface electrodes102 via RF wires (not shown) extending through the clamping members 304.In the illustrated embodiment, the respective surface electrodes 102 arecoupled to the RF generator 104 in a bipolar arrangement, i.e., onesurface electrode 102 is coupled to the first pole of the RF generator104, and the other surface electrode 102 is coupled to the second poleof the RF generator 104. The needle electrodes 112 on each of thesurface electrodes 102 can be selectively activated using the electricalinterface on the respective surface electrode 102. Alternatively, onlyone of the surface electrodes 102 is activated, in which case, the othersurface electrode merely serves as a means for stabilizing the othersurface electrode 102 within the tissue. The needle electrodes 112 ofthe active surface electrode 102 can be designed to be placed in abipolar arrangement or a monopolar arrangement. Deactivation of thesurface electrode 102 can be accomplished via the electrical interface,or alternatively, a stabilizing member with non-active needles, or astabilizing member with no tissue penetrating needles, can be usedinstead of a potentially active surface electrode 102.

Referring now to FIGS. 19 and 20, operation of the tissue ablationsystem 300 is described in treating a treatment region TR, such as atumor, located between opposing surfaces S1 and S2 of tissue T, e.g., anorgan. The treatment region TR also has opposing surfaces S3 and S4.

First, the electrical interface(s) on the surface electrodes 102 areconfigured, based on the shape of the treatment region TR and whether amonopolar or a bipolar arrangement is desired. The surface electrodes102 are then positioned, such that they are respectively adjacent theopposing surfaces S1 and S2 of the tissue T, as illustrated in FIG. 19.Preferably, access to the tissue T is gained through a surgical openingmade through the skin of the patient. The clamping device 302 can beclosed, while introduced through the opening, and then opened in orderto place the tissue T between the opposing surface electrodes 102.Alternatively, each individual clamping member 304 and associatedsurface electrode 102 can be introduced through two respectivelaparoscopes and then subsequently assembled at the pivot point 306.

Next, the clamping device 302 is closed, such that the needle electrodes112 of the respective surface electrodes 102 penetrate through thesurfaces S1 and S2 into the tissue T, as illustrated in FIG. 20. Asillustrated, the application of pressure by the clamping device 302,causes the tissue T in contact with the surface electrodes 102 tocompress. Once the needle electrodes 112 are embedded into the tissue T,the distances that the needle electrodes 112 extend from the base 108 ofthe surface electrode 102 are individually adjusted in the mannerpreviously described. If provided, the optional insulating sleeves canalso be adjusted. The RF generator 104 is then connected to the clampingdevice 300, and then operated to ablate the treatment region TR,resulting in the formation of a lesion that preferably encompasses theentirety of the treatment region TR. If the treatment region TR issubstantially larger than that which the surface electrode 102 cancover, thereby resulting in a treatment region TR that is only partiallyablated, the clamping device 302 can be opened to release the needleelectrodes 102 from the tissue T, and then reapplied to a differentportion of the tissue T.

Although particular embodiments of the present invention have been shownand described, it should be understood that the above discussion is notintended to limit the present invention to these embodiments. It will beobvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present invention. Thus, the present invention is intended to coveralternatives, modifications, and equivalents that may fall within thespirit and scope of the present invention as defined by the claims.

1. A surface electrode for ablating tissue, comprising: a base having asurface; a plurality of tissue penetrating needle electrodes extendingfrom the surface of the base an adjustable distance; and an electricalinterface coupled to the plurality of needle electrodes. 2.-75.(canceled)